1. Field of the Invention
The present invention relates to an electromedical implant for monitoring a thoracic property of a living being, wherein the implant has a housing. The invention further relates to a monitoring system including the electromedical implant.
2. Description of the Background Art
An electromedical implant can be purely a monitoring implant, or a monitoring and therapy implant. Contrary to therapy implants, such as implantable cardiac stimulators or the like, an electromedical implant for monitoring a thoracic property of a living being (patient), which is referred to as a monitoring implant, provides no therapy options. A monitoring implant can also be useful and important for patients having no therapy indication in order to draw conclusions about the health of the patient by monitoring a thoracic property. For example, an indication for electrotherapy may not be apparent, or a type of electrotherapy prior to conducting the same may not be specifiable in detail, until the patient has been monitored for an extended period using the monitoring implant.
Existing approaches for monitoring a thoracic property, which is to say the pulse transit time, of a living being largely employ non-invasive systems, as those which are described, for example, in U.S. Pat. Nos. 7,029,447 or 6,748,262 or 5,743,856 for monitoring cardiac or epithoracic, peripheral blood flows. Non-invasive systems, however, are cumbersome to handle when it comes to monitoring a thoracic property of a living being for an extended period. On the other hand, a cardiac invasive system, as that described in DE 36 29 587 A1, which corresponds to U.S. Pat. No. 4,674,518, is not an option for a patient having no therapeutic indication. The implantation of probes in the heart, for example for determining an ECG signal using a cardiac stimulator, is associated with risks for the patient and complex. At the same time, patients without indication for electrotherapy constitute a significant portion of patients suffering from cardiac insufficiency.
The desire is therefore to provide an electromedical implant for monitoring a thoracic property of a living being, which also enables long-term, comparatively simple monitoring without requiring cardiac invasion.
An electromedical implant mentioned at the beginning is known, for example, from US 2009/0062667 A1, wherein ultimately, for monitoring an arterial blood pressure a pulse transit time is determined from the pulse peak arrival times of two signals. Using subcutaneously implanted electrodes, a first signal in the form of an electrocardiogram is determined, which is indicative of an electrical activity of a patient's heart, which is to say the blood ejected from the heart. In addition, a sensor in the form of a photoplethysmography sensor implanted in the pectoral region is used to obtain corresponding signal which is indicative of a mechanical activity of a patient's heart, which is to say the arrival of a blood pulse in the pectoral region. This concept can be implemented as an implantable monitor having no electrotherapy device.
U.S. Pat. No. 5,331,966 discloses an electromedical implant comprising a detector arrangement, which includes an array of relatively closely spaced subcutaneous electrodes for detecting electrical cardiac signals, wherein a selected electrode pair for recording what is referred to as a far-field electrocardiogram is provided. The array of electrodes is attached on or in the vicinity of the implant outside of a patient's heart, wherein the electrodes are disposed in a circular shape and in a triangular arrangement on the surface of the implant in order to record a vectorial subcutaneous far-field electrocardiogram.
US 2008/0234591 A1 and US 2008/0183225 A1 disclose an electromedical implant having a shroud assembly which surrounds the implant and again comprises three electrodes having an oval shape, which are disposed on a narrow side of the implant and provided for recording an extracardiac far-field cardiogram.
US 2004/0225329 A1 discloses an electromedical implant having a plurality of subcutaneous electrodes, which are disposed as part of an array on a lateral surface of the implant and interact with surface electrodes attached to the thorax of the patient for recording a subcutaneous electrocardiogram.
While the above approaches of subcutaneous electromedical implants, in principle, have proven useful for monitoring a thoracic property of a living being, they are in need of improvement.